Rebecca Hasson, PhD

OccupationDirector, Childhood Disparities Research Laboratory at the University of Michigan

FocusInsulin Resistance/Prediabetes

ADA Research FundingJunior Faculty

Type 2 diabetes is a modern epidemic, but an enduring puzzle is why it’s spreading faster in some groups than in others. In the United States, 1 in 2 African Americans and Latinos will develop type 2 diabetes in their lifetimes; the risk for whites is 1 in 3.

Researchers once thought genes might account for the dramatic differences. Studies trying to tease out the reasons for disparities in type 2 diabetes risk have also examined factors such as physical activity, nutrition, and family history of diabetes.

But there’s increasing evidence that the environment we live in plays a bigger role than the genes we’re born with. The everyday stresses people face, such as poverty and discrimination—factors that some people live with more than others—may be taking a physical toll. “There’s substantial evidence to demonstrate the environment we live in has direct impacts on our health,” says exercise physiologist Rebecca Hasson, PhD, director of the Childhood Disparities Research Laboratory at the University of Michigan.

One reason is a hormone called cortisol. Cortisol puts gas in the body’s tank: It tells the body to increase blood glucose, directs cells to resist insulin’s signals to absorb and store blood glucose in favor of keeping it available for muscles to burn, and prompts cravings for high-calorie foods. It’s released in times of stress to help supply the body with as much energy as possible, as part of the “fight or flight” response to immediate threats. “Cortisol is a biomarker of stress,” Hasson says.

That’s all good, if you’re being attacked by a lion and need energy to escape. But other things can trigger cortisol, too. “Those energy substrates are mobilized so you can run away,” Hasson says. “But if you don’t, or can’t run away—you’re late for school, someone’s pointing a gun at you, you can’t pay your bills—you’re always in this high-alert situation, whether or not you’re conscious of it.”

When cortisol levels are consistently high but there’s no physical activity to buffer the effects of chronic stress, the consequences may contribute to type 2 diabetes. Higher cortisol results in higher insulin resistance, for example, forcing the pancreas to produce more insulin to get a response. With ongoing insulin resistance, the insulin-producing beta cells wear out, causing type 2 diabetes.

If we know chronic stress makes people sick, is it possible blacks and Latinos are sicker than whites because they’re more stressed? They’re more likely to be poor or live in poor neighborhoods, so they’re more likely to be exposed to the chronic stressors of poverty—and to cortisol, with all of its negative effects. Exposure to discrimination, too, can be a stressful experience. “Overall, ethnic minorities have much higher cortisol levels and exposure than whites,” Hasson says.

With the help of a grant from the American Diabetes Association and funding from the Prince Hall Shriners, Hasson is working with 150 obese children between ages 14 and 18 to measure the links between stress, race, and type 2 diabetes risk directly. The teenage years, Hasson says, are a “perfect biological and social storm” where school, family, and neighborhood stresses pile on to already raging hormones.

Part of the study involves gathering information on family income, diet, family life, and any racial discrimination participants might have experienced, all to get a sense of reasons they might feel stressed.

Because the stress levels teens self-report aren’t always reliable, Hasson also measures cortisol as a reference, asking participants to spit into a test tube five times a day and measuring cortisol levels in saliva. “You can’t rely on somebody’s perception of stress in their life. Kids exposed to a lot of stress underreport,” she says.

Overall, Hasson has found that the African American and Latino children in the study have higher cortisol levels. By following them over time, she hopes to find out if their cortisol levels and other measures of stress are connected to higher rates of type 2 diabetes. “If there are ethnic differences in the stress pathways, that could help guide our intervention,” Hasson says. “We’d have to start asking ourselves how we can reduce stress in their lives.”

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